1. Field of the Invention
The present invention relates to a timing generator and a timing generating method generating strobe signals of desired timing and a test apparatus testing a device under test.
2. Description of Related Art
Conventionally, there has been known a method using PLL (Phase Lock Loop) as a method generating clock signals of a desired phase. The method is a method superimposing a desired voltage on a control voltage to be supplied to a voltage-controlled oscillator in the PLL in order to shift phases of clock signals according to the superimposed voltage.
Now, since a related patent document is not recognized, the description is omitted.
However, when shifting phases of clock signals by means of a voltage-controlled oscillator, some errors may be observed between a set shift amount and a real shift amount. For this reason, an initialization has conventionally been performed by previously measuring relation between a voltage being superimposed on a control voltage of a voltage-controlled oscillator and a real shift amount.
For example, the relation between a superimposed voltage and a phase shift amount can be measured by superimposing two kinds of voltages on a control voltage of a voltage-controlled oscillator and detecting an amount of phase shift for each superimposed voltage. In this case, it is necessary to accurately detect the amount of phase shift. However, in order to accurately detect the amount of phase shift, it is necessary to measure the amount of phase shift, e.g., using a loop circuit. Therefore, a measurement error has been observed due to a delay in the loop circuit.